1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a handoff system and method among heterogeneous networks, and to a mobile terminal and operation method thereof using the same, capable of performing seamless handoffs to the most appropriate network in aspect of resources of data-link layers and network layers.
2. Description of the Related Art
Recently, with performance improvements of mobile terminals such as handheld computers and Personal Digital Assistants (PDA's), more users use the wireless internet, and advancements of wireless communication technologies provide the users with various types of network environments.
FIG. 1 is a view for showing environments for heterogeneous networks.
The wireless Internet users can use various types of network environments. As shown in FIG. 1, heterogeneous network environments can include Institute of Electrical and Electronics Engineers (IEEE) 802.11 20, IEEE 802.16 30, Wideband-CDMA (W-CDMA) 40, and so on, and, in such wireless internet environments, a mobile terminal 10 can frequently move around and change its network connection point.
In order to enable the mobile terminal 10 to communicate over the wireless Internet, even though the mobile terminal 10 moves to a certain network area beyond its current network area, the mobile terminal 10 in the certain network area should receive the same high quality Internet services as in the current network area.
That is, the mobile terminal 10 has to perform seamless communications, so that a handoff concept is applied. The handoff refers to a function of transferring a process for communications from an access node for the current network area to an access node for another network area.
Meanwhile, recently, the developments of Internet technologies generalize real-time multi-media services such as Video On Demand (VOD), Audio On Demand (AOD), videophones, video chatting, and the like. Specifically, the mobile terminal 10 can be used to get real-time multi-media services together with advancements of the wireless Internet technologies and improvements of the data processing capacity of the mobile terminal 10.
Together with the advancements of the technologies as above, users can be provided with real-time multi-media services through the mobile terminal 10 while moving. Accordingly, lots of studies are continuing on methods enabling effective handoffs to be performed as users roam around.
Heterogeneous networks support different bandwidths one another, but most of the conventional handoff-processing methods for the mobile terminal 10 do not take into consideration the differences among the transmission bandwidths supported by networks to which the mobile terminal 10 is connected before and after the mobile terminal 10 roams around.
For example, if the mobile terminal 10 moves from an area of the Wireless Local Area Network (WLAN) to an area of the 3 Generation Partnership Project (3GPP) network, there exists a transmission bandwidth difference among the two networks since the bandwidth of the WLAN is larger than or equal to 384 Kbps and the bandwidth of the 3GPP network is smaller than 384 Kbps.
As above, if the bandwidth supported by a network before the movement is larger than the bandwidth supported by a network after the movement, the loss of data packets caused by the bandwidth difference cannot be compensated for. Accordingly, there exists a problem of degrading the qualities of real-time multi-media services.
Further, the conventional handoff-processing method for the mobile terminal 10 can be described as below in brief. That is, when the mobile terminal 10 requests a handoff to the access node in a network area to which the mobile terminal 10 moves, the access node allows the handoff if the resources of the network to which the access node belongs are sufficient.
Failing to reserve resources in the network to which the mobile terminal 10 is going to move, the mobile terminal 10 requests again the handoff until finding out another network that has sufficient resources. Thus, there exists a problem that it takes time excessively for retries for resources reservations until the mobile terminal 10 finds out a network having sufficient resources as networks are more overlapped in number.